Method and apparatus for communication based on short transmission time intervals in a wireless communication system

ABSTRACT

Embodiments of the present disclosure relate to the communication processes in a wireless communication system based on short TTIs. According to one embodiment of the present disclosure, there provide a method for communication by a base station. The method comprise: receiving, from a user equipment, an uplink demodulation reference signal, DMRS, in an uplink transmission time interval, TTI, of an uplink subframe, which supports two or more uplink TTIs. At least one uplink TTI supported by the uplink subframe is configured to only transmit uplink control information and/or uplink data without any uplink DMRS. In the other aspects of the present disclosure, there also provides methods for communication by a user equipment and corresponding apparatuses.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 16/953,057 filed on Nov. 19, 2020, which is acontinuation application of U.S. patent application Ser. No. 16/234,103filed on Dec. 27, 2018, which is a continuation application of U.S.patent application Ser. No. 16/072,543 which is issued as U.S. Pat. No.10,841,907, which is a National Stage Entry of international applicationPCT/CN2016/073221 filed on Feb. 2, 2016, the disclosures of all of whichare incorporated in their entirety by reference herein.

TECHNICAL FIELD

The present disclosure generally relates to wireless communication,particularly to methods and apparatuses for demodulation referencesignal (DMRS) transmission based on shortened Transmission TimeIntervals (TTIs) in a communication system.

BACKGROUND

This section is intended to provide a background to the variousembodiments of the invention that are described in this disclosure. Thedescription herein may include concepts that could be pursued, but arenot necessarily ones that have been previously conceived or pursued.Therefore, unless otherwise indicated herein, what is described in thissection is not prior art to the description and/or claims of thisdisclosure and is not admitted to be prior art by the mere inclusion inthis section.

A long-term evolution (LTE) system, initiated by the third generationpartnership project (3GPP), is now being regarded as a new radiointerface and radio network architecture that provides a high data rate,low latency, packet optimization, and improved system capacity andcoverage. In the LTE system, an evolved universal terrestrial radioaccess network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs)and communicates with a plurality of mobile stations, also referred asuser equipments (UEs). The radio protocol stacks of the E-UTRAN is givenincluding a radio resource control layer (RRC), a packet dataconvergence protocol layer (PDCP), a radio link control layer (RLC), amedia access control layer (MAC), and a physical layer (PHY).

In 3GPP radio access network (RAN) LTE systems, the node can be acombination of Evolved Universal Terrestrial Radio Access Network(E-UTRAN) Node Bs (also commonly denoted as evolved Node Bs, enhancedNode Bs, eNodeBs, or eNBs) and Radio Network Controllers (RNCs), whichcommunicates with the wireless device, known as a user equipment (UE).The downlink (DL) transmission can be a communication from the node(e.g., eNodeB) to the wireless device (e.g., UE), and the uplink (UL)transmission can be a communication from the wireless device to thenode.

In LTE, data can be transmitted from the UE to the eNodeB via a physicaluplink shared channel (PUSCH). The PUSCH carries scheduled data trafficand possible control signaling. The PUSCH can be carried in subframes ofa radio frame. Further, data can also be transmitted from the eNodeB toUE via a physical downlink shared channel (PDSCH). PDSCH is also carriedin one ms subframes and is downlink scheduled over respective TTIs. TheUE can transmit acknowledgement (ACK)/non-acknowledgement (NACK)feedback to the base station via a physical uplink control channel(PUCCH), which may be used to carry uplink control information.Conventionally, a one millisecond (ms) subframe containing 14 symbols,can only allow a one ms TTI, which is the smallest time unit to schedulethe DL and UL transmission.

Demodulation reference signals (DMRS) are used in Time DivisionDuplexing (TDD) or/and Frequency Division Duplexing (FDD) wirelesscommunication systems to determine the quality of downlink and uplinkchannels.

According to the current 3GPP specifications, DMRS signals areconfigured with PUCCH/PUSCH/PDSCH channels at the time. 1A-1Cschematically illustrate example patterns of DMRS in PUCCH, PUSCH, PDSCHstructures of existing LTE systems. In every TTI that supports 14symbols, multiple symbols need to be assigned to DMRS transmission.

In the 3GPP RAN #67 meeting, the Study Item on “Study on Latencyreduction techniques for LTE” was approved. For RAN1, TTI shortening andreduced processing times should be studied and documented at least infollowing aspects:

-   -   study feasibility and performance of TTI lengths between 0.Sms        and one OFDM symbol is studied, taking into account impact on        reference signals and physical layer control signaling;    -   backwards compatibility shall be preserved, thus allowing normal        operation of pre-Rel 13 UEs on the same carrier.

Nevertheless, it is concluded in the study that “byreducingtheTTIlength, the networkcanscheduletheUEfaster, which reducesthe round trip time (RTT). A reduction in RTT increases the TCPthroughput. A reduction of TTI length may also increase the systemcapacity for small data transmission.”

Therefore, there is a need to provide solutions for DMRS communicationbased on short TTIs in a wireless communication system.

SUMMARY

It is noted that since the number of symbols in one TTI is reduced inview of latency reduction technique, if DMRS signals are introduced foreach TTI, DMRS overhead must be considerable, especially for short TTIincluding 1 or 2 symbols. In addition, channel condition may not varymuch, especially for continuous scheduling or short TTI in highfrequency. In that sense, some DMRS may not be necessary in demodulatingcontrol information or data.

To solve the above problem, one or more method and apparatus embodimentsaccording to the present disclosure aim to provide solutions for DMRScommunication based on shortened TTIs. Other features and advantages ofembodiments of the present disclosure will also be understood from thefollowing description of specific embodiments when read in conjunctionwith the accompanying drawings, which illustrate the principles ofembodiments of the present disclosure.

According to the first aspect of the present disclosure, there isprovided a method for communication by a base station operating in awireless communication system. The method comprises: receiving, from auser equipment, an uplink demodulation reference signal, DMRS, in anuplink transmission time interval, TTI, of an uplink subframe, whichsupports two or more uplink TTIs. At least one uplink TTI supported bythe uplink subframe is configured to only transmit uplink controlinformation and/or uplink data without any uplink DMRS.

According to the second aspect of the present disclosure, there isprovided a method for communication by a base station operating in awireless communication system. The method comprises: transmitting, to auser equipment, a downlink DMRS in a downlink TTI of a downlink subframewhich supports two or more downlink TTIs. At least one ownlink TTIsupported by the downlink subframe is configured to only transmitdownlink control information and/or downlink data without any downlinkDMRS.

According to the third aspect of the present disclosure, there isprovided a method for communication by a user equipment operating in awireless communication system. The method comprises: transmitting, to abase station, an uplink demodulation reference signal, DMRS, in anuplink transmission time interval, TTI, of an uplink subframe, whichsupports two or more uplink TTIs. At least one uplink TTI supported bythe uplink subframe is configured to only transmit uplink controlinformation and/or uplink data without any uplink DMRS.

According to the fourth aspect of the present disclosure, there isprovided a method for communication by a user equipment operating in awireless communication system. The method comprises: receiving, from abase station, a downlink DMRS in a downlink TTI of a downlink subframewhich supports two or more downlink TTIs. At least one downlink TTIafter the downlink TTI in which the downlink DMRS is received isarranged not to transmit any downlink DMRS.

According to further aspects of the present disclosure, there provides abase station. The base station comprises a transmitting unit and areceiving unit, which are adapted to perform functions as describedabove in the first, second aspects of the present disclosure.

According to further aspects of the present disclosure, there provides auser equipment. The user equipment comprises a transmitting unit and areceiving unit, which are adapted to perform functions as describedabove in the third, fourth aspects of the present disclosure.

According to further aspects of the present disclosure, there alsoprovides a base station. The base station comprises processing meansadapted to perform the methods for communication by a base stationaccording to any of various embodiments of the present disclosure.

According to further aspects of the present disclosure, there alsoprovides a user equipment. The user equipment comprises processing meansadapted to perform the methods for communication by a user equipmentaccording to any of various embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Inventive features regarded as the characteristics of the presentinvention are set forth in the appended claims. However, the presentinvention, its implementation mode, other objectives, features andadvantages will be better understood through reading the followingdetailed description on the exemplary embodiments with reference to theaccompanying drawings, where in the drawings:

FIGS. 1A-1C schematically illustrate example DMRS patterns configured inPUCCH, PUSCH, PDSCH, respectively, for a wireless communication system;

FIGS. 2A-2B are a diagram schematically illustrating example DMRSstructures applicable to multiple short TTIs according to embodiments ofthe present disclosure;

FIGS. 3A and 3B are diagram schematically illustrating example DMRSstructures with candidate DMRS positions and fixed DMRS positionsaccording to one or more embodiments of the present disclosure;

FIGS. 4A-4C are diagrams schematically illustrating example DMRSstructure suitable for a 1-symbol-based TTI according to one or moreembodiments of the present disclosure;

FIG. 5 is a diagram schematically illustrating a method forcommunication by a base station according to one or more embodiments ofthe present disclosure;

FIG. 6 is a diagram schematically illustrating a method forcommunication by a user equipment according to one or more embodimentsof the present disclosure;

FIGS. 7A-7C are diagrams schematically illustrating example UL and DLsubframes with uplink DMRS according to one or more embodiments of thepresent disclosure;

FIG. 8 is a diagram schematically illustrating example UL and DLsubframes with uplink DMRS according to a further embodiment of thepresent disclosure;

FIG. 9 is a diagram schematically illustrating example scheme fordemodulating PUCCH channels based on uplink DMRS according to one ormore embodiments of the present disclosure;

FIGS. 10A-10C are diagrams schematically illustrating example UL and DLsubframes with uplink DMRS according to one or more embodiments of thepresent disclosure;

FIG. 11 is a diagram schematically illustrating a method forcommunication by a base station according to further one or moreembodiments of the present disclosure;

FIG. 12 is a diagram schematically illustrating a method forcommunication by a user equipment according to further one or moreembodiments of the present disclosure;

FIGS. 13A-13B are diagrams schematically illustrating example UL and DLsubframes with downlink DMRS according to further one or moreembodiments of the present disclosure;

FIG. 14 is a block diagram schematically illustrating a base stationaccording to further one or more embodiments of the present disclosure;and

FIG. 15 is a block diagram schematically illustrating a user equipmentaccording to further one or more embodiments of the present disclosure.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be describedwith reference to the accompanying drawings. In the followingdescription, many specific details are illustrated so as to understandthe present disclosure more comprehensively. However, it is apparent tothe skilled in the art that implementation of the present invention maynot have these details. Additionally, it should be understood that thepresent invention is not limited to the particular embodiments asintroduced here. On the contrary, any combination of the followingfeatures and elements may be considered to implement and practice thepresent invention, regardless of whether they involve differentembodiments. For example, while it is described below in the context of5G cellular communication system for illustrative purposes, thoseskilled in the art will recognize that one or more embodiments of thepresent disclosure can also be applied to various other types ofcellular communication systems. Thus, the following aspects, features,embodiments and advantages are only for illustrative purposes, andshould not be understood as elements or limitations of the appendedclaims, unless otherwise explicitly specified in the claims.

A user equipment (UE) may comprise, be implemented as, or known as anaccess terminal, a subscriber station, a subscriber unit, a mobilestation, a remote station, a remote terminal, a user terminal, a useragent, a user device, a user station, or some other terminology.

In some implementations, a user equipment may comprise a cellulartelephone, a cordless telephone, a Session Initiation Protocol (SIP)phone, a personal digital assistant (PDA), a handheld device havingwireless connection capability, a Station (STA), or some other suitableprocessing device connected to a wireless modem. Accordingly, one ormore aspects taught herein maybe incorporated into a phone (e.g., acellular phone or smart phone), a computer (e.g., a laptop), a portablecommunication device, a portable computing device (e.g., a personal dataassistant), an entertainment device (e.g., a music or video device, or asatellite radio), a global positioning system device, or any othersuitable device that is configured to communicate via a wireless orwired medium. In some aspects the node is a wireless node. Such wirelessnode may provide, for example, connectivity for or to a network (e.g., awide area network such as the Internet or a cellular network) via awired or wireless communication link.

A base station (BS) may comprise, be implemented as, or known as NodeB,Radio Network Controller (RNC), eNodeB (eNB), Base Station Controller(BSC), Base Transceiver Station (BTS), Transceiver Function (TF), RadioRouter, Radio Transceiver, Basic Service Set (BSS), Extended Service Set(ESS), Radio Base Station (RBS), or some other terminology.

As discussed above, the number of symbols in one UL/DL TTI needs to bereduced in order to reduce latency. However, in the existing LTEtechnique, DMRS is introduced for each TTI and occupy at least onesymbol. DMRS overhead consumes radio resources significantly both intime and frequency domain, especially in the condition that a short TTIincludes 1 or 2 symbols. In addition, channel condition may not varyvery much among short TTIs, especially for continuous scheduling or inhigh frequency. In that sense, it may cause the problem in radioresource efficiency to configure DMRS together with various physicalchannels in each TTI.

To solve the above problem, one or more method and apparatus embodimentsaccording to the present disclosure aim to provide solutions for DMRScommunication based on shortened TTIs, where UL/DL DMRS can betransmitted independently from transmission of respective physicalchannels, such as, physical uplink shared channel (PUSCH), physicaluplink control channel (PUCCH), physical downlink shared channel(PDSCH). In other words, the transmission of DMRS is controlled byseparate means from that controls the transmission of respectivephysical channels. According to various embodiments of the presentdisclosure, DMRS may be triggered to be transmitted dynamically.According to additional or alternative embodiments of the presentdisclosure, transmission of DMRS is set with one or more periodicpatterns, which may be configured with high layer signaling. The meansfor controlling DMRS transmission independently can be applied in anysuitable combination way. As a consequence, for example, some of TTIismay be transmitted without DMRS in a short TTI, while some of TTIs maybe controlled to transmit additional DMRS in candidate DMRS positions.

FIGS. 2A and 2B are diagrams schematically illustrating example DMRSstructures applicable to multiple short TTIs according to embodiments ofthe present disclosure. For the purpose of conciseness of thedescription, let us suppose TTIs discussed with reference to FIGS. 2Aand 2B includes two or more symbols.

FIG. 2A shows a subframe structure where DMRS may be controlled to onlybe transmitted in some TTIs, while there is no DMRS transmission in someother TTIs.

In dashed block 201, example structures for TTIs with DMRS transmissionare illustrated. In one example, DMRS may occupy one or multiple symbolsof one TTI, and the remaining symbols of the TTI can be used to transmitdata or control information depending upon the type of the physicalchannel that is currently scheduled in this TTI. In another example,DMRS may be sparse in time and/or frequency domain, which, for example,occupy part of frequency resources of one or more symbols in one TTI.The remaining symbols of the TTI can be used to transmit data or controlinformation depending upon the specific type of the physical channelthat is currently scheduled in the TTI.

Dashed block 202 provides example structures for no-DMRS TTIs. Whenthere is no DMRS transmission in a TTI, in one example, the DMRSpositions may be reserved and kept empty even if the remaining symbolsof the TTI are occupied by data or control information. In this example,those predefined radio resources are dedicated to transmit DMRS andcannot be used to transmit data or control information. It will be moreefficient if data or control information can use those radio resourcesfor DMRS transmission if there is actually no DMRS transmitted in thisTTI. In that example, all symbols of the TTI can be assigned to data orcontrol information transmission. It should be appreciated that DMRSstructure for short TTIs may also be designed in a way of any suitablecombination of the above resource-reserved and the resource-sharedmodes.

FIG. 2B shows a subframe structure where in some TTIs, additional DMRStransmission may be activated than other normal TTIs.

As shown in FIG. 2B, candidate DMRS position may be predefined in a TTI.When DMRS transmission is triggered or configured by a higher layersignaling, one or several DMRS positions may be selected from thosecandidate DMRS positions based on the triggering information or thehigher layer signaling. For the purpose of backward compatibility, thenew DMRS structure may support the fixed DMRS positions as specified inexisting LTE (as discussed with reference to FIGS. 1A-1C). Whenadditional DMRS is triggered or configured by a higher layer signaling,besides the fixed DMRS positions, extra DMRS may be transmitted as need.

FIGS. 3A and 3B are diagram schematically illustrating example DMRSstructures with candidate DMRS positions and fixed DMRS positionsaccording to one or more embodiments of the present disclosure.

In some implementation, when frequency offset estimation is needed, thenone additional DMRS can be configured (by a trigger or periodically).Otherwise, only original fixed DMRS is transmitted (history frequencyoffset can be reused). FIG. 3A illustrates a subframe structure withfixed DMRS positions such as legacy DMRS position. As shown in FIG. 3A,a TTI is constituted with 4 symbols, in which one symbol in the fixedDMRS is shared by two consecutive TTIs. Additional DMRS positions may bearranged in each TTI. By separate controlling means of, for example,triggering by a specified trigger or transmitting in a periodic mannerconfigured by a higher layer signaling, DMRS transmission may beactivated in some of additional candidate DMRS positions. For example,as shown in FIG. 3B, the additional DMRS position in the first TTI asshown is configured to transmit DMRS. In the following TTIs as shown, noDMRS transmission is configured in the additional DMRS positions, sothat DMRS is only transmitted in the fixed positions in these TTIs.

FIGS. 4A-4C are diagrams schematically illustrating example DMRSstructure suitable for a 1-symbol-based TTI according to one or moreembodiments of the present disclosure.

When DMRS is configured in a TTI constituted with only one symbol, DMRSmay be multiplexed with data or control information (e.g., PUSCH, PUSCH,PDSCH) in the same symbol. FIGS. 4A and 4B show two differentmultiplexing manners for DMRS and data/control information. In theexample as shown in FIG. 4A, the 1-symbol-based TTI with DMRSmultiplexed with data/control information may adopt a structuredifferent from those symbols without DMRS. The 1-symbol-based TTIoccupies more frequency resource than a symbol without multiplexed DMRS.In the example of FIG. 4B, the 1-symbol-based TTI with DMRS mayalternatively

FIG. 4C illustrates another example where DMRS is transmitted indifferent symbols from physical channels (PUSCH/PUCCH/PDSCH). As shownin FIG. 4C, DMRS occupies all resource of a 1-symbol-based TTI and maybe transmitted prior to the data or control information. There is nomultiplexing between data/control information and DMRS in a1-symbol-based TTI.

More generally, in a L-symbol-based TTI, the number of DMRS (K, K>=O)may be configured dynamically, for example, by downlink controlinformation (DCI) and/or semi-statically, for example, by higher layersignaling; and L-K symbols are configured for data/control information.Alternatively, in a TTI, DMRS can be sparse and multiplexed withdata/control information in frequency domain. In some implementations,different TTIs or TTI groups may have independent number of DMRS. Forexample, TTI groups may be consecutive TTIs or periodic TTIs withdifferent period and/or offset. TTI group size may also be configured,e.g. dynamically indicated in DCI or semi-statically indicated withhigher layer information. The independent number of DMRS may also beconfigured dynamically by DCI and/or semi-statically by higher layersignaling. As discussed above, DMRS may be configured in some candidatepositions. Additionally or alternatively, newly triggered DMRS may havea different pattern as configured.

FIG. 5 is a diagram schematically illustrating a method 500 forcommunication by a base station according to one or more embodiments ofthe present disclosure. The method 500 of FIG. 5 describes the processof uplink DMRS transmission from the perspective of the base station. Asshown in FIG. 5, in step S510, the base station receives, from a userequipment, an uplink DMRS in an uplink TTI of an uplink subframe. Theuplink subframe supports two or more uplink TTIs.

The transmission of the uplink DMRS is controlled independently from thetransmission of an uplink physical channel. At least one uplink TTIsupported by the uplink subframe may be configured to only transmituplink control information and/or uplink data without any uplink DMRS.The uplink DMRS may adopt any suitable DMRS structure as described withreference to FIGS. 1-4.

According to one or more embodiments of the present disclosure, themethod 500 may further comprise a step (not shown) of transmitting, tothe user equipment, an uplink DMRS trigger to enable the transmission ofthe uplink DMRS in the uplink TTI of the uplink subframe. The uplinkDMRS trigger may be carried in a downlink TTI of a downlink subframewhich supports two or more downlink TTIs. As an example, the uplink DMRStrigger may be one or several bits to enable the transmission and/orconfiguration of corresponding DMRS. According to one or moreembodiments of the present disclosure, the uplink DMRS trigger mayinclude information on how to configure the uplink DMRS to betransmitted from the user equipment to the base station. As discussedwith reference to FIGS. 2-4, several type of DMRS configurationinformation may be included in the trigger. By way of example, theuplink DMRS trigger may include information indicative of, but notlimited to, at least one following items: the number of symbols that theuplink DMRS occupies; time duration of the triggered uplink DMRS;resource allocation for the uplink DMRS; and candidate symbol position(s) on which the uplink DMRS occupies in the uplink TTI.

According to one or more additional or alternative embodiments of thepresent disclosure, the uplink DMRS may be received from the userequipment periodically. The uplink DMRS is controlled to be transmittedin a periodic way by means of, for example, a higher layer signaling.

FIG. 6 is a diagram schematically illustrating a method forcommunication by a user equipment according to one or more embodimentsof the present disclosure. The method 600 of FIG. 6 describes theprocess of uplink DMRS transmission from the perspective of the userequipment. As shown in FIG. 6, the user equipment transmits, in stepS610, to the base station the uplink DMRS in the uplink TTI of the ULsubframe supports two or more uplink TTIs.

The transmission of the uplink DMRS is controlled independently from thetransmission of an uplink physical channel. At least one uplink TTIsupported by the uplink subframe may be configured to only transmituplink control information and/or uplink data without any uplink DMRS.The DMRS may adopt any suitable DMRS structure as described withreference to FIGS. 1-4.

Similarly, according to one or more embodiments of the presentdisclosure, the method 600 may further comprise a step (not shown) ofreceiving, from a base station, an uplink DMRS trigger to enable thetransmission of the uplink DMRS in the uplink TTI of the uplinksubframe. The uplink DMRS trigger may be carried in a downlink TTI of adownlink subframe which supports two or more downlink TTIs. As anexample, the uplink DMRS trigger may be one or several bits to enablethe transmission and/or configuration of corresponding DMRS. Accordingto one or more embodiments of the present disclosure, the uplink DMRStrigger may include information on how to configure the uplink DMRS tobe transmitted from the user equipment to the base station. As discussedwith reference to FIGS. 2-4, several type of DMRS configurationinformation may be included in the trigger. By way of example, thetrigger may indicate which candidate symbol position(s) the uplink DMRSoccupies in the uplink TTI. The user equipment may trigger thetransmission of uplink DMRS according to the configuration informationindicated in the received trigger.

According to one or more additional or alternative of the presentdisclosure, the uplink DMRS may be received from the user equipmentperiodically. The uplink DMRS is controlled to be transmitted in aperiodic way by means of, for example, a higher layer signaling.

FIGS. 7A-7C are diagrams schematically illustrating example UL and DLsubframes with uplink DMRS according to one or more embodiments of thepresent disclosure, where uplink DMRS is transmitted during an uplinkdata scheduling process.

During an uplink data scheduling process, the base station may transmitthe uplink DMRS trigger to the user equipment by including it in DCI foruplink data scheduling (i.e., UL grant). By way of example, one or more

bits may be added to existing DCI format O and/or format 4 to representthe uplink DMRS trigger. At that case, the downlink TTI is arranged toschedule both uplink data (PUSCH) and triggered uplink DMRS.

As shown in FIG. 7A, the base station transmits DCI for uplink datascheduling (i.e., UL grant) in DL TTI n. As a response, the userequipment will transmit the uplink data transmission (i.e., PUSCH) in ULTTI n+k, where k is an integer and may be normally set as 4 in a FDDsystem, and predefined according to the uplink/downlink configurationsin a TDD system. When detecting the uplink DMRS trigger included in theDCI received in DL TTI n, the user equipment may transmit, in UL TTIn+k, the uplink DMRS according to the DMRS configuration informationcontained in the trigger. In this way, the uplink DMRS and PUSCH sharethe same UL TTI n+k. As described in FIGS. 2-4, the uplink DMRS anduplink data may be multiplexed in frequency domain and/or the uplinkDMRS occupies M symbols of UL TTI n+k and the remaining symbols of ULTTI n+k is used to transmit the scheduled uplink data. As a consequent,the PUSCH in UL TTI n+k may be shortened to occupy (L-M) symbols.Alternatively, PUSCH and DMRS may be staggered in frequency domain, justas shown in FIG. 4A or 4B.

When the channel conditions change a little, the base station may decidenot to trigger the transmission of uplink DMRS, the channel conditionestimation can be obtained based on the previous DMRS. For example, inDL TTI n+1, DL TTI n+2, no trigger is contained in DCI. Therefore, theuser equipment will transmit scheduled uplink data in UL TTI n+k+1, ULTTI n+k+2, in which there is no UL DMRS transmitted.

FIG. 7B shows another example for dealing with the situation where thebase station schedules uplink data and triggers uplink DMRS in the sameDL TTI. In this example, the uplink DMRS may be configured to betransmitted in advance. As shown in FIG. 7B, it may be predefined thatwhen receiving the uplink DMRS trigger together with the DCI in DL TTIn, the user equipment can transmit the triggered DMRS in UL TTI n+k−1.Then in UL TTI n+k, the user equipment transmits the uplink datascheduled by the DCI. Here, n represents the TTI number of the downlinkTTI in which downlink control information for uplink data scheduling istransmitted; and k is a predefined integer which represents a predefinednumber of TTIs for scheduling.

FIG. 7C shows yet another example for dealing with the situation wherethe base station schedules uplink data and triggers uplink DMRS in thesame DL TTI. In this example, transmission of scheduled uplink data maybe delayed one TTI after the uplink DMRS is transmitted. As shown inFIG. 7C, it may be predefined that when receiving the uplink DMRStrigger together with the DCI in DL TTI n, the user equipment cantransmit the triggered DMRS in UL TTI n+k. Then in UL TTI n+k+1, theuser equipment transmits the uplink data scheduled by the DCI. Here, nrepresents the TTI number of the downlink TTI in which downlink controlinformation for uplink data scheduling is transmitted; and k is apredefined integer which represents a predefined number of TTIs forscheduling. In those TTIs without DMRS transmission, the base stationmay demodulate the received PUSCH with reference to the previouslyreceived uplink DMRS.

Here, those skilled in the art should appreciate that similar schemes asdiscussed with reference to FIGS. 7A-7C may also be applied to thoseembodiments where periodic uplink DMRS is configured semi-statically byhigher layer signaling, in order to solve the problem caused by thecollision between transmissions of the uplink DMRS and uplink data(e.g., PUSCH).

In some embodiments, the uplink DMRS trigger may be received separatelyfrom the DCI for uplink data scheduling. That means, the uplink DMRStrigger may be send separately in a TTI without DCI for uplinkscheduling.

FIG. 8 is a diagram schematically illustrating example UL and DLsubframes with uplink DMRS according to a further embodiment of thepresent disclosure where the uplink DMRS trigger is transmittedseparately in DL TTI n. As shown in FIG. 8, in such embodiments, thetriggered uplink DMRS will not collide with scheduled uplink data. Forexample, in response to the trigger received in DL TTI n, the userequipment may transmit uplink DMRS in UL TTI n+k. And in response to DCIfor uplink data scheduling received in DL TTI n+1, the user equipmentmay transmit scheduled uplink data in UL TTI n+k+1.

In an implementation, when the user equipment needs PUSCH transmission,after schedule request, the base station may trigger uplink DMRS bysending an uplink DMRS trigger in a separate TTI. In the uplink DMRStrigger, resource allocation field may be contained. After the DMRStrigger, the base station can schedule PUSCH by sending compact DCI foruplink data scheduling, because the user equipment may refer to theresource allocation field in the uplink DMRS trigger to performsubsequent uplink data transmission.

During a downlink data scheduling process, uplink DMRS may also beneeded to demodulate the uplink control channels (e.g., PUCCH).Therefore, according to one or more embodiments of the presentdisclosure, the base station may transmit to the user equipment anuplink DMRS trigger as need so as to trigger the transmission of theuplink DMRS. Additionally or alternatively, the uplink DMRS may becontrolled to be transmitted in a periodic way by means of, for example,a higher layer signaling so as to meet the requirement of PUCCHdemodulation.

FIG. 9 is a diagram schematically illustrating example scheme fordemodulating PUCCH channels based on uplink DMRS according to one ormore embodiments of the present disclosure. As shown in FIG. 9, theuplink DMRS is transmitted independently with PUCCH. For example, periodand/or offset of uplink DMRS and PUCCH (including CQI/PMI/RI) may bedifferent. In another example, uplink DMRS is aperiodic, because it maybe triggered by the base station, for example, in DCI information.

Since PUCCH is be modulated on transformed or same ZC sequence as theuplink DMRS, after demodulation the PUCCH information, the remainingsequence can be used as demodulation reference signal for channelestimation, which provides reference to next subsequent PUCCH and/oruplink data. That means, a physical uplink control channel may bedemodulated based on the uplink DMRS. And then, one or more subsequentphysical uplink control channel may be demodulated based on thepreviously received uplink DMRS and/or the demodulated physical uplinkcontrol channel.

FIGS. 10A-10C are diagrams schematically illustrating example UL and DLsubframes with uplink DMRS according to one or more embodiments of thepresent disclosure where uplink DMRS is transmitted during a downlinkdata scheduling process.

In a downlink data scheduling process, the user equipment needs totransmit ACK/NACK feedback information to the base station in PUCCH. AsACK/NACK feedback information is related to downlink data scheduling,both the user equipment and the base station is aware of which UL TTIthe ACK/NACK feedback information will be transmitted. When the basestation needs uplink DMRS from the user equipment for demodulating theACK/NACK feedback information, the base station may trigger thetransmission of uplink DMRS by transmitting a downlink DMRS trigger orconfigure a periodic uplink DMRS with semi-static radio resource control(RRC) signaling.

According to one or more embodiments of the present disclosure,transmission of uplink DMRS may be triggered with an uplink DMRStrigger. The base station may send the uplink DMRS trigger together withDCI for downlink data scheduling (i.e., DL schedule) in a downlink TTI.By way of example, one or more bits may be added to existing DCI fordownlink data scheduling to represent the uplink DMRS trigger. At thatcase, the downlink TTI is arranged to schedule both downlink data(PDSCH) and triggered uplink DMRS.

As shown in FIG. 10A, the base station transmits DCI for downlink datascheduling (i.e., DL grant) in DL TTI n. As a response, the userequipment will transmit the ACK/NACK feedback for downlink datascheduling (in PUCCH) in UL TTI n+k, where k is an integer, which may benormally set as 4 in a FDD system, and predefined according to theuplink/downlink configuration in a TDD system. When detecting the uplinkDMRS trigger included in the DCI received in DL TTI n, the userequipment may transmit, in UL TTI n+k, the uplink DMRS according to theDMRS configuration information contained in 30 the trigger. In this way,the uplink DMRS and the ACK/NACK feedback information share the same ULTTI n+k. As described in FIGS. 2-4, the uplink DMRS and ACK/NACKfeedback information may be multiplexed in frequency domain and/or theuplink DMRS occupies M symbols of UL TTI n+k and the remaining symbolsof UL TTI n+k is used to transmit the ACK/NACK feedback information. Asa consequent, the PUCCH in UL TTI n+k may be shortened to occupy (L-M)symbols. Alternatively, PUCCH and DMRS may be staggered in frequencydomain, just as shown in FIG. 4A or 4B.

When there is no need to estimate channel conditions, the base stationmay decide not to trigger the transmission of uplink DMRS. For example,in DL TTI n+1, DL TTI n+2, no trigger is contained in DCI. Therefore,the user equipment will transmit scheduled ACK/NACK feedback informationin UL TTI n+k+1, UL TTI n+k+2, in which there is no UL DMRS transmitted.In those TTIs without DMRS transmission, the base station may demodulatethe received ACK/NACK feedback information with reference to thepreviously received uplink DMRS.

FIG. 10B shows another example for dealing with the situation where thebase station schedules downlink data and triggers uplink DMRS in thesame DL TTI. In this example, the uplink DMRS may be configured to betransmitted in advance. As shown in FIG. 10B, it may be predefined thatwhen receiving the uplink DMRS trigger together with the DCI fordownlink scheduling in DL TTI n, the user equipment can transmit thetriggered DMRS in UL TTI n+k−1. Then in UL TTI n+k, the user equipmenttransmits the CK/NACK feedback information for the downlink datascheduling. Here, n represents the TTI number of the downlink TTI inwhich downlink control information for downlink data scheduling istransmitted; and k is a predefined integer which represents a predefinednumber of TTIs for scheduling.

FIG. 10C shows yet another example for dealing with the situation wherethe base station schedules downlink data and triggers uplink DMRS in thesame DL TTI. In this example, transmission of corresponding ACK/NACKfeedback information for the downlink data scheduling may be delayed oneTTI after the uplink DMRS is transmitted. As shown in FIG. 10C, it maybe predefined that when receiving the uplink DMRS trigger together withthe downlink data in DL TTI n, the user equipment can firstly transmitthe triggered DMRS in UL TTI n+k. Then in UL TTI n+k+1, the userequipment transmits the ACK/NACK feedback information for the downlinkdata. Here, n represents the TTI number of the downlink TTI in whichdownlink control information for downlink data scheduling istransmitted; and k is a predefined integer which represents a predefinednumber of TTIs for scheduling.

Here, those skilled in the art should appreciate that similar schemes asdiscussed with reference to FIGS. 10A-10C may also be applied to thoseembodiments where periodic uplink DMRS is configured semi-statically byhigher layer signaling, in order to solve the problem caused by thecollision between transmissions of the uplink DMRS and ACK/NACK feedbackinformation (e.g., PUCCH).

According to other embodiments of the present disclosure, the uplinkDMRS trigger may not be carried in DCI for downlink data scheduling. Thebase station may use a separate DL TTI to transmit the uplink DMRStrigger. In such embodiments, the triggered uplink DMRS may not collidewith ACK/NACK feedback information for downlink data scheduling.

For example, in response to the trigger received in DL TTI n, the userequipment may transmit uplink DMRS in UL TTI n+k. And in response todownlink data received in DL TTI n+1, the user equipment may transmitscheduled uplink data in UL TTI n+k+1.

FIG. 11 is a diagram schematically illustrating a method 1100 forcommunication by a base station according to further one or moreembodiments of the present disclosure where downlink. The method 1100 ofFIG. 11 describes the process of downlink DMRS transmission from theperspective of the base station. As shown in FIG. 11, in step S1110, thebase station transmits, to a user equipment, a downlink DMRS in adownlink TTI of a downlink subframe. The downlink subframe supports twoor more downlink TTIs.

FIG. 12 is a diagram schematically illustrating a method forcommunication by a user equipment according to further one or moreembodiments of the present disclosure. The method 1200 of FIG. 12describes the process of downlink DMRS transmission from the perspectiveof the user equipment. As shown in FIG. 12, in step S1210, the userequipment receives from a base station, an uplink demodulation referencesignal, DMRS, in an uplink transmission time interval, TTI, of an uplinksubframe, which supports two or more uplink TTIs

The transmission of the downlink DMRS is controlled independently fromthe transmission of a downlink physical channel (such as PDSCH). In thatway, it is possible that some downlink TTI supported by the downlinksubframe may be configured to only transmit downlink control informationand/or downlink data without any downlink DMRS. The downlink DMRS mayadopt any suitable DMRS structure as described with reference to FIGS.1-4.

According to one or more embodiments of the present disclosure, adownlink DMRS trigger to enable transmission of the downlink DMRS may betransmitted from the base station to the user equipment. As an example,the downlink DMRS trigger may be one or several bits to enable thetransmission and/or configuration of corresponding DMRS. As discussedwith reference to FIGS. 2-4, several type of DMRS configurationinformation may be included in the trigger. By way of example, thedownlink DMRS trigger may include information indicative of, but notlimited to, at least one following items: the number of symbols that thedownlink DMRS occupies; time duration of the triggered downlink DMRS;resource allocation for the downlink DMRS; and candidate symbol position(s) on which the downlink DMRS occupies in the downlink TTI.

FIGS. 13A-13B are diagrams schematically illustrating example UL and DLsubframes with downlink DMRS according to further one or moreembodiments of the present disclosure where downlink DMRS is enabled bya downlink DMRS trigger.

According to one or more embodiments of the present disclosure, thedownlink DMRS trigger to enable transmission of the downlink DMRS may betransmitted together with DCI for downlink data scheduling in the samedownlink TTI. As shown in FIG. 13A, in DL TTI n, the user equipment maytransmit the downlink DMRS to the user equipment by including it in theDCI for downlink data scheduling. In some implementations, at least partof the downlink DMRS may be sparse-multiplexed with downlink data in thedownlink TTI of the downlink subframe. Additionally or alternatively,the downlink DMRS may occupy one or more symbols of the downlink TTI andthe remaining symbols may be used for downlink data transmission. Innext downlink TTI n+1, the base station may decide not to trigger thetransmission of downlink DMRS, because the user equipment may demodulatedownlink data transmitted in downlink TTI n+1 based on the previouslyreceived downlink DMRS.

According to additional or alternative embodiments, the downlink DMRStrigger to enable transmission of the downlink DMRS may be transmittedseparately from DCI for downlink data scheduling. As shown in FIG. 13B,in downlink TTI n, a DMRS trigger is transmitted to indicate thedownlink DMRS configuration information to the user equipment. In thesame TTI n, the base station transmits the downlink DMRS according tothe configuration information included in the downlink DMRS trigger.According to some implementation, in view of the information of resourceallocation contained in the downlink DMRS trigger, the base station mayschedule PDSCH in at least one subsequent TTI by sending compact DCI fordownlink data scheduling, because the user equipment may refer to theresource allocation field in the downlink DMRS trigger to performsubsequent downlink data transmission.

In order to communicate the downlink DMRS independently from schedulinga physical downlink data channel (e.g., PDSCH), according to one or moreadditional or alternative embodiments of the present disclosure, thedownlink DMRS may be transmitted from the base station to the userequipment periodically. The downlink DMRS is controlled to betransmitted in a periodic way by means of, for example, a higher layersignaling.

FIG. 14 is a block diagram schematically illustrating a base stationaccording to further one or more embodiments of the present disclosure.

As shown in FIG. 14, the base station 1400 is configured to communicatewith one or more user equipments based downlink and uplink subframestructures having short TTIs. The base station 1400 comprises: atransmitting unit 1410 and a receiving unit 1420. The base station 600may also comprise suitable radio frequency transceivers (not shown inFIG. 14) that may be selectively coupled with one or more antenna(s)(not shown in FIG. 14) which are used to transmit signals to, andreceive signals from, one or more user equipments.

The base station 1400 comprises a processor 141, which may include oneor more microprocessor or microcontrollers, as well as other digitalhardware, which may include digital signal processors (DSPs),special-purpose digital logic, and the like. The processor 141 may beconfigured to execute program code stored in memory (not shown in FIG.14), which may include one or several types of memory such as read-onlymemory (ROM), random-access memory, cache memory, flash memory devices,optical storage devices, etc. Program code stored in memory includesprogram instructions for executing one or more telecommunications and/ordata communications protocols as well as instructions for carrying outoneor more of the techniques described herein, in several embodiments.In some implementations, the processor 141 maybe used to cause thetransmitting unit 1410 and the receiving unit 1420 to performcorresponding functions according one or more embodiments of the presentdisclosure.

According to embodiments of one aspect of the present disclosure, thereceiving unit 1420 is configured to receive, from a user equipment, anuplink DMRS in an uplink TTI of an uplink subframe, which supports twoor more uplink TTIs. At least one uplink TTI supported by the uplinksubframe is configured to only transmit uplink control informationand/or uplink data without any uplink DMRS.

According to one or more embodiments of this aspect of the presentdisclosure, the transmitting unit 1510 may be configured to transmit, tothe user equipment, an uplink DMRS trigger to enable the transmission ofthe uplink DMRS in the uplink TTI of the uplink subframe. The uplinkDMRS trigger maybe carried in a downlink TTI of a downlink subframewhich supports two or more downlink TTIs. In some embodiments, theuplink DMRS trigger may include information indicative of at least onefollowing items: a number of symbols that the uplink DMRS occupies; atime duration of the triggered uplink DMRS; resource allocation for theuplink DMRS; and candidate symbol position (s) on which the uplink DMRSoccupies in the uplink TTI.

According to one or more embodiments of this aspect of the presentdisclosure, the uplink DMRS trigger maybe included in downlink controlinformation for uplink data scheduling. Alternatively, the uplink DMRStrigger maybe received separately from downlink control information foruplink data scheduling.

According to one or more embodiments of this aspect of the presentdisclosure, the uplink DMRS may be received from the user equipmentperiodically.

In some embodiments of this aspect of the present disclosure, thereceiving unit 1420 may be further configured to receive scheduleduplink data in the uplink TTIn+k in which the uplink DMRS is received;or receive scheduled uplink data in an uplink TTI n+k immediately afterthe uplink TTI n+k−1 in which the uplink DMRS is received; or receivescheduled uplink data in an uplink TTIn+k+1 immediately after the uplinkTTI n+k in which the uplink DMRS is received. Here, n represents the TTInumber of the downlink TTI in which downlink control information foruplink data scheduling is transmitted; k represents a predefined numberof TTIs for uplink scheduling.

According to one or more embodiments of this aspect of the presentdisclosure, a physical uplink control channel may be demodulated basedon the uplink DMRS. In some embodiments, a further physical uplinkcontrol channel maybe demodulated based on the uplink DMRS and/or thedemodulated physical uplink control channel.

According to one or more embodiments of this aspect of the presentdisclosure, the transmitting unit 1410 may be configured to transmit theuplink DMRS trigger included in downlink control information fordownlink data scheduling.

According to one or more embodiments of this aspect of the presentdisclosure, the receiving unit 1420 may be further configured to receiveacknowledgement, ACK, /non-acknowledgement, NACK, feedback informationfor the downlink data scheduling in the uplink TTI n+k in which theuplink DMRS is received; or receive ACK/NACK feedback information forthe downlink data scheduling in an uplink TTI n+k immediately after theuplink TTI n+k−1 in which the uplink DMRS is received; or receiveACK/NACK feedback information for the downlink data scheduling in anuplink TTI n+k+1 immediately after the uplink TTI n+k in which theuplink DMRS is received. Here, n represents the TTI number of thedownlink TTI in which downlink data for downlink data scheduling istransmitted; k represents a predefined number of TTIs for downlinkscheduling.

According to one or more embodiments of this aspect of the presentdisclosure, the transmitting unit 1410 may be configured to transmit theuplink DMRS trigger separately from downlink control information fordownlink data scheduling.

According to embodiments of another aspect of the present disclosure,the transmitting unit 1410 may be configured to transmit, to a userequipment, a downlink DMRS in a downlink TTI of a downlink subframewhich supports two or more downlink TTIs. At least one downlink TTIsupported by the downlink subframe is configured to only transmitdownlink control information and/or downlink data without any downlinkDMRS.

According to embodiments of this aspect of the present disclosure, thetransmitting unit 1410 may be configured to transmit a downlink DMRStrigger to enable transmission of the downlink DMRS included in downlinkcontrol information for downlink data scheduling. In some embodiments,the transmitting unit 1410 may be further configured to transmit atleast part of the downlink DMRS which is sparse-multiplexed withdownlink data in the downlink TTI of the downlink subframe.

According to alternative embodiments of this aspect of the presentdisclosure, the transmitting unit 1410 may be configured to transmit adownlink DMRS trigger to enable transmission of the downlink DMRSseparately from downlink control information for downlink datascheduling.

According to embodiments of this aspect of the present disclosure, thedownlink DMRS trigger may include information indicative of at least onefollowing items: a number of symbols that the downlink DMRS occupies; atime duration of the triggered downlink DMRS; resource allocation forthe downlink DMRS; and candidate symbol position (s) on which thedownlink DMRS occupies in the uplink TTI.

According to embodiments of this aspect of the present disclosure, thetransmitting unit 1410 may be configured to transmit the downlink DMRSto the user equipment periodically.

FIG. 15 is a block diagram schematically illustrating a user equipmentaccording to further oneor more embodiments of the present disclosure.

As shown in FIG. 15, the user equipment 1500 is configured tocommunicate with a base station based downlink and uplink subframestructures having short TTIs. The user equipment 1500 comprises areceiving unit 1510 and a transmitting unit 1520. The user equipment1500 may also comprise multiple suitable radio frequency transceivers(not shown in FIG. 15) that maybe operably coupled with one or moreantenna(s) (not shown in FIG. 15) which are used to transmit signals to,and receive signals from, other radio nodes such as a NodeB, an eNodeBor a WiFi AP.

The user equipment 1500 comprises a processor 151, which may include oneor more microprocessor or microcontrollers, as well as other digitalhardware, which may include digital signal processors (DSPs),special-purpose digital logic, and the like. The processor 151 may beconfigured to execute program code stored in memory (not shown in FIG.15), which may include one or several types of memory such as read-onlymemory (ROM), random-access memory, cache memory, flash memory devices,optical storage devices, etc. Program code stored in memory includesprogram instructions for executing one or more telecommunications and/ordata communications protocols as well as instructions for carrying outone or more of the techniques described herein, in several embodiments.In some implementations, the processor 151 may be used to cause thereceiving unit 1510 and the transmitting unit 1520 to performcorresponding functions according one or more embodiments of the presentdisclosure.

According to embodiments of one aspect of the present disclosure, atransmitting unit 1420 is configured to transmit, to a base station, anuplink DMRS in an uplink TTI of an uplink subframe, which supports twoor more uplink TTIs. At least one uplink TTI supported by the uplinksubframe is configured to only transmit uplink control informationand/or uplink data without any uplink DMRS.

According to embodiments of this aspect of the present disclosure, thereceiving unit 1500 is configured to receive, from a base station, anuplink DMRS trigger to enable the transmission of the uplink DMRS in theuplink TTI of the uplink subframe. The uplink DMRS trigger may becarried in a downlink TTI of a downlink subframe which supports two ormore downlink TTIs. According to some embodiments, the uplink DMRStrigger may include information indicative of at least one followingitems: a number of symbols that the uplink DMRS occupies; a timeduration of the triggered uplink DMRS; resource allocation for theuplink DMRS; and candidate symbol position(s) on which the uplink DMRSoccupies in the uplink TTI.

According to embodiments of this aspect of the present disclosure, thereceiving unit 1510 may be configured to receive the uplink DMRS triggerwhich is included in downlink control information for uplink datascheduling. In some alternative embodiments, the receiving unit 1510 maybe configured to receive the uplink DMRS trigger separately fromdownlink control information for uplink data scheduling.

According to embodiments of this aspect of the present disclosure, thetransmitting unit 1520 may be configured to transmit the uplink DMRS tothe base station periodically.

In some embodiments of this aspect of the present disclosure, thetransmitting unit 1520 may be further configured to: transmit scheduleduplink data in the uplink TTI n+k in which the uplink DMRS is received;or transmit scheduled uplink data in an uplink TTI n+k immediately afterthe uplink TTI n+k−1 in which the uplink DMRS is received; or transmitscheduled uplink data in an uplink TTI n+k+1 immediately after theuplink TTI n+k in which the uplink DMRS is received. Here, n representsthe TTI number of the downlink TTI in which downlink control informationfor uplink data scheduling is transmitted; k represents a predefinednumber of TTIs for uplink scheduling.

According to one or more embodiments of this aspect of the presentdisclosure, the user equipment 1500 may configured to demodulate aphysical uplink control channel based on the uplink DMRS. In someembodiments, the user equipment 1500 may configured to demodulate afurther physical uplink control channel based on the uplink DMRS and/orthe demodulated physical uplink control channel.

According to one or more embodiments of this aspect of the presentdisclosure, the receiving unit 1510 may be configured to receive theuplink DMRS trigger included in downlink control information fordownlink data scheduling.

According to one or more embodiments of this aspect of the presentdisclosure, the transmitting unit maybe further configured to: transmitACK/NACK feedback information for the downlink data scheduling in theuplink TTI n+k in which the uplink DMRS is received; or transmitACK/NACK feedback information for the downlink data scheduling in anuplink TTI n+k immediately after the uplink TTI n+k−1 in which theuplink DMRS is received; or transmit ACK/NACK feedback information forthe downlink data scheduling in an uplink TTI n+k+1 immediately afterthe uplink TTI n+k in which the uplink DMRS is received. Here, nrepresents the TTI number of the downlink TTI in which downlink data fordownlink data scheduling is transmitted; k represents a predefinednumber of TTIs for downlink scheduling.

According to one or more embodiments of this aspect of the presentdisclosure, the receiving unit 1510 may be configured to receive theuplink DMRS trigger separately from downlink control information fordownlink data scheduling.

According to embodiments of another aspect of the present disclosure,the receiving unit 1510 is configured to receive, from a base station, adownlink DMRS in a downlink TTI of a downlink subframe which supportstwo or more downlink TTIs. At least one downlink TTI after the downlinkTTI in which the downlink DMRS is received is arranged not to transmitany downlink DMRS.

According to embodiments of this aspect of the present disclosure, thereceiving unit 1510 may be configured to receive a downlink DMRS triggerto enable transmission of the downlink DMRS included in downlink controlinformation for downlink data scheduling. In some embodiments, thereceiving unit 1510 may be configured to receive at least part of thedownlink DMRS which is sparse-multiplexed with downlink data in thedownlink TTI of the downlink subframe.

According to embodiments of this aspect of the present disclosure, thereceiving unit 1510 may be configured to receive a downlink DMRS triggerto enable transmission of the downlink DMRS separately from downlinkcontrol information for downlink data scheduling.

According to embodiments of this aspect of the present disclosure, thedownlink DMRS trigger may include information indicative of at least onefollowing items: a number of symbols that the downlink DMRS occupies; atime duration of the triggered downlink DMRS; resource allocation forthe downlink DMRS; and candidate symbol position (s) on which thedownlink DMRS occupies in the uplink TTI.

According to embodiments of this aspect of the present disclosure, thereceiving unit 1510 may be configured to receive the downlink DMRS fromthe base station periodically.

In general, the various exemplary embodiments may be implemented inhardware or special purpose circuits, software, logical or anycombination thereof. For example, some aspects maybe implemented inhardware, while other aspects maybe implemented in firmware or softwarewhich may be executed by a controller, microprocessor or other computingdevice, although the disclosure is not limited thereto. While variousaspects of the exemplary embodiments of this disclosure may beillustrated and described as block and signaling diagrams, it is wellunderstood that these blocks, apparatus, systems, techniques or methodsdescribed herein maybe implemented in, as on-limiting examples,hardware, software, firmware, special purpose circuits or logical,general purpose hardware or controller or other computing devices, orsome combination thereof.

As such, it should be appreciated that at least some aspects of theexemplary embodiments of the disclosure may be practiced in variouscomponents such as integrated circuit chips and modules. As well knownin the art, the design of integrated circuits is by and large a highlyautomated process.

The present disclosure may also be embodied in the computer programproduct which comprises all features capable of implementing the methodas depicted herein and may implement the method when loaded to thecomputer system.

The present disclosure has been specifically illustrated and explainedwith reference to the preferred embodiments. The skilled in the artshould understand various changes thereto in form and details maybe madewithout departing from the spirit and scope of the present disclosure.

What is claimed is:
 1. A method for a User Equipment (UE), the methodcomprising: receiving, from a base station, first information in ahigher layer signaling, the first information indicating for a group ofa plurality of candidates of second position(s) for at least one secondDemodulation Reference Signal (DMRS)(s); receiving, from the basestation, second information with a Downlink Control Information (DCI)format, wherein the second information is regarding to scheduledresource for Physical Downlink Shared Channel (PDSCH); and determining,based on the first information and the second information, whether theat least one second DMRS(s) for the PDSCH is mapped to at least onesymbol at the second position(s) among the plurality of candidates inaddition to a first DMRS for the PDSCH mapped to one symbol at firstposition, wherein the first position and the second position(s) arewithin a scheduling time unit.
 2. The method according to claim 1,further comprising: receiving, from the base station, the first DMRS andthe at least one second DMRS(s) in a case where the at least one secondDMRS(s) is mapped.
 3. The method according to claim 2, wherein the firstDMRS is mapped to one symbol at the first position regardless of thefirst information.
 4. The method according to claim 1, furthercomprising: receiving, from the base station, the first DMRS without theat least one the second DMRS(s) being received within the schedulingtime unit in a case where the at least one second DMRS(s) is not mapped.5. The method according to claim 1, wherein the first position is symbol0 or symbol
 3. 6. The method according to claim 1, further comprising:receiving third information indicating the first position.
 7. The methodaccording to claim 2, wherein the first position is prior to all of thesecond position(s) within the scheduling time unit in time domain. 8.The method according to claim 2, wherein at the first position or thesecond position(s), the first DMRS or the at least one second DMRS(s) ismapped to one resource element from among every two resource elements infrequency domain, and wherein remaining resource elements not used forthe first DMRS or the second DMRS(s) at the first position or the secondposition(s) are used for transmission of the PDSCH.
 9. The methodaccording to claim 1, wherein the PDSCH is not present during timeduration of the first position or the second position(s).
 10. The methodaccording to claim 2, wherein the first position or the secondposition(s) are prior to resources for the PDSCH within the schedulingtime unit.
 11. A method for a base station, the method comprising:transmitting, to a User Equipment (UE), first information in a higherlayer signaling, the first information indicating for a group of aplurality of candidates of second position(s) for at least one secondDemodulation Reference Signal (DMRS)(s); and transmitting, to the UE,second information with a Downlink Control Information (DCI) format,wherein the second information is regarding to scheduled resource forPhysical Downlink Shared Channel (PDSCH); wherein whether to transmit,to the UE, the at least one second DMRS(s) for the PDSCH being mapped toat least one symbol at the second position(s) among the plurality ofcandidates in addition to a first DMRS for the PDSCH being mapped to onesymbol at first position, corresponds to the first information and thesecond information, wherein the first position and the secondposition(s) are within a scheduling time unit.
 12. The method accordingto claim 11, further comprising: transmitting, to the UE, the first DMRSand the at least one second DMRS(s) in a case where the at least onesecond DMRS(s) is mapped.
 13. The method according to claim 12, whereinthe first DMRS is mapped to one symbol at the first position regardlessof the first information.
 14. The method according to claim 11, furthercomprising: receiving, from the base station, the first DMRS without theat least one the second DMRS(s) being received within the schedulingtime unit in a case where the at least one second DMRS(s) is not mapped.15. The method according to claim 11, wherein the first position issymbol 0 or symbol
 3. 16. The method according to claim 11, furthercomprising: receiving third information indicating the first position.17. The method according to claim 12, wherein the first position isprior to all of the second position(s) within the scheduling time unitin time domain.
 18. The method according to claim 12, wherein at thefirst position or the second position(s), the first DMRS or the at leastone second DMRS(s) is mapped to one resource element from among everytwo resource elements in frequency domain, and wherein remainingresource elements not used for the first DMRS or the second DMRS(s) atthe first position or the second position(s) are used for transmissionof the PDSCH.
 19. The method according to claim 11, wherein the PDSCH isnot present during time duration of the first position or the secondposition(s).
 20. The method according to claim 12, wherein the firstposition or the second position(s) are prior to resources for the PDSCHwithin the scheduling time unit.
 21. A User Equipment (UE) comprising: atransceiver; and a processor; wherein the transceiver is configured to:receive, from a base station, first information in a higher layersignaling, the first information indicating for a group of a pluralityof candidates of second position(s) for at least one second DemodulationReference Signal (DMRS)(s); and receive, from the base station, secondinformation with a Downlink Control Information (DCI) format, whereinthe second information is regarding to scheduled resource for PhysicalDownlink Shared Channel (PDSCH); wherein the processor is configured to:determine, based on the first information and the second information,whether the at least one second DMRS(s) for the PDSCH is mapped to atleast one symbol at the second position(s) among the plurality ofcandidates in addition to a first DMRS for the PDSCH mapped to onesymbol at first position, wherein the first position and the secondposition(s) are within a scheduling time unit.
 22. A base stationcomprising: a transceiver; and a processor; wherein the transceiver isconfigured to: transmit, to a User Equipment (UE), first information ina higher layer signaling, the first information indicating for a groupof a plurality of candidates of second position(s) for at least onesecond Demodulation Reference Signal (DMRS)(s); and transmit, to the UE,second information with a Downlink Control Information (DCI) format,wherein the second information is regarding to scheduled resource forPhysical Downlink Shared Channel (PDSCH); wherein whether to transmit,to the UE, the at least one second DMRS(s) for the PDSCH being mapped toat least one symbol at the second position(s) among the plurality ofcandidates in addition to a first DMRS for the PDSCH being mapped to onesymbol at first position, corresponds to the first information and thesecond information, wherein the first position and the secondposition(s) are within a scheduling time unit.